JPH0520463B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for producing a crosslinked foam that is made of a mixture of vinyl acetate-ethylene copolymer and a large amount of inorganic material, and has a high expansion ratio, flame retardancy, and low smoke properties. In general, plastic foams are used in a wide range of applications such as building materials, packaging materials, and flotation materials because they are lightweight and have excellent properties such as heat insulation, shock absorption, and sound absorption. Among these, polyolefin foams are widely used in a wide range of applications because of their superior chemical, mechanical, and electrical properties compared to other plastics. However, a major drawback of this polyolefin is that it is extremely flammable, and in recent years, from a safety standpoint to prevent disasters caused by fire, strict flame retardant properties have been required for materials using these polyolefins. There is. As a method for making polyolefin flame retardant, a method is known in which a halogen flame retardant or a relatively large amount of inorganic powder is mixed with polyolefin. The former method of mixing halogen-based flame retardants has the advantage that flame-retardant products can be obtained relatively easily, but once this flame-retardant material is combusted in a fire, halogenated hydrogen Because they generate extremely large amounts of smoke containing harmful gases such as, this can actually increase the danger to humans. Moreover, even if direct damage from the heat of the fire was avoided, serious drawbacks such as the corrosion of expensive equipment by the corrosive hydrogen halide generated could not be avoided. On the other hand, the latter method of making polyolefin flame retardant by adding inorganic substances does not have such a dangerous effect and is also an excellent method from the viewpoint of resource saving. However, since a large amount of inorganic powder is blended, foaming gas escapes significantly during foaming, making it difficult to produce a high-magnification foam, and a continuous sheet-like high-magnification foam of particularly good quality has not been realized. For example, examples 2 and 3 of the prior art are as follows. According to Japanese Patent Publication No. 51-37300, a method is proposed in which a foaming agent and a crosslinking agent are added to a composition consisting of a polyethylene resin and aluminum hydroxide, and the composition is heated and foamed. In this method, a composition prepared by adding 0.25 parts by weight of a crosslinking agent and 3.5 parts by weight of a blowing agent to a composition of 40 parts by weight of high-pressure polyethylene and 60 parts by weight of aluminum hydroxide is placed in a closed mold,
By releasing the mold all at once after heating, a foam with a maximum expansion ratio of 17.5 times (density 0.134 g/cm ³ ) was obtained. For example, a large amount of inorganic powder is added to vinyl chloride resin and kneaded in a closed kneader, then a solvent in which liquefied butane or the like is dissolved is added and mixed, and then poured into a mold under closed pressure. A method of producing a foam having a specific gravity of 0.15 to 0.18 by two-step heat foam molding is described in Japanese Patent Application Laid-open No. 49371/1983. Further, Japanese Patent Application Publication No. 48-85649 discloses that thermoplastic resins containing ethylene-vinyl acetate copolymers
10 to 5% by weight and 50 to 90% by weight of an inorganic filler containing calcium sulfite as an essential component, a crosslinking agent and a foaming agent are added, mixed uniformly and formed into a plate shape, which is then pressed under pressure. After heating at 200℃ for 10 minutes,
It is described that a foam with an apparent specific gravity of 0.08 to 0.18 was obtained by rapidly removing the pressure. In this case, as in the above-mentioned known example, the foaming composition is filled into a closed container such as a mold, and in order to suppress free expansion, pressure is applied from the outside, and the crosslinking agent and foaming agent are decomposed in this state. Afterwards, the pressure is rapidly removed to obtain a foam. These methods all involve filling a mold with a foamable material and heating and foaming it under pressure, and it is difficult to obtain a foam with a high ratio of closed cells exceeding 20 times, and it is difficult to produce a long foam sheet. It was something that could not be manufactured. The present inventors investigated filling compositions of various thermoplastic resins, mainly olefin polymers, and inorganic powders, and found that ethylene-vinyl acetate copolymers do not exhibit tensile properties even when filled with a large amount of inorganic powders. It has been found that the polymer exhibits relatively little deterioration in mechanical properties and maintains moldability, making it an excellent polymer for use in highly-filled inorganic materials. It has also been found that when aluminum hydroxide powder is highly loaded, it exhibits significantly higher flame retardancy than polyethylene, polypropylene, etc. due to its synergistic effect with vinyl acetate groups. Therefore, the present inventors have developed a flame-retardant foam that is inexpensive, contributes to resource conservation, and has low smoke emission, by foaming an ethylene-vinyl acetate copolymer composition containing a high degree of inorganic powder. The present invention was achieved as a result of trying to realize the present invention. (Disclosure of the present invention) The present invention provides a method for producing a foam that can efficiently obtain a crosslinked foam with a high expansion ratio made of a composition containing a large amount of inorganic powder etc. with a small amount of ionizing radiation irradiation. . The foam obtained by the production method of the present invention is a high-magnification foam containing a large amount of inorganic material. In many cases, the total amount of other additive components, mainly inorganic substances, is greater than the polymer component, so from the viewpoint of the components, it can be said to be an inorganic form. While it has the flexibility and processability of polymers, it also has the properties of inorganic materials. The proportion of polymer is very small, often 20
g/ or less (2vo1% or less as specific gravity 1). The main characteristics of the foam obtained by the manufacturing method of the present invention are listed below. (1) Despite containing a large amount of inorganic powder, the foaming ratio (composition density/foam density ratio) is 40.
It is an extremely highly cross-linked foam that is more than twice as strong. (2) It is a continuous sheet-like foam with no length limit. (3) It has an extremely high Oxygen Index (usually 30 to 75) and does not exhibit any melt dripping phenomenon that can cause fire spread during forced combustion. (4) Extremely low smoke and heat generation during forced combustion. (5) Extremely high heat resistance as shown by dimensional shrinkage rate during heating. Crosslinked polyethylene foam deforms to the extent that it does not lose its original shape at temperatures above 130°C, but this foam only exhibits shrinkage deformation of a few percent even at 150 to 180°C. Additionally, during forced combustion, the surrounding area of the foam that is hit by the fire does not undergo any abnormal deformation and retains its shape. As a supplement to item (4), it is noteworthy that although this foam is a flammable polymer, it has extremely high flame retardancy and low smoke emission. Therefore, JIS A1321-1975 is required for insulation iron plates made by bonding this foam with a thickness of about 4 mm to galvanized iron plates.
"Flame retardant test method for building interior materials and construction methods"
When conducting a flame retardancy test according to the surface test in Section 3, the number of smoke systems per unit area (C _A ), which is an indicator of the amount of smoke generated during combustion, and the exhaust temperature curve, which is an indicator of combustion heat, are The area (tdθ) of the part surrounded by the exhaust gas temperature curve exceeding the standard temperature curve and the standard temperature curve is C _A ≦30 and tdθ = 0, and ranks highest in terms of smoke generation and heat generation under the same law. It is something that will be done. (That is, it satisfies the conditions that can be defined as class 1 flame retardancy) This is not possible with conventionally known polyolefin foams, and is only possible with the foam of the present invention. Regarding the oxygen index in item (3), JIS
According to D1201-1973 "Flammability Test Method for Organic Materials for Automotive Interiors", materials with an oxygen index exceeding 30 are classified as flame retardant class 1, which is the highest ranking category in this test. The foam of the present invention falls under this category. The ionizing radiation crosslinking method of the present invention is as follows. That is, a resin component consisting of an ethylene-vinyl acetate copolymer alone or a blend of the copolymer and a thermoplastic resin having a vinyl acetate content of 40 to 90% by weight.
100 parts by weight, 50 to 500 parts by weight of inorganic powder, blowing agent 5
~50 parts by weight and 1 to 5 parts by weight of a carboxylic acid metal salt are added and kneaded to form a composition, then irradiated with ionizing radiation to crosslink, and then heated to a temperature higher than the decomposition temperature of the blowing agent to foam. 1. A method for producing a foam made of an inorganic-containing ethylene-vinyl acetate copolymer. Generally, those containing 5 to 40% by weight of vinyl acetate are crystalline, and those containing 40 to 90% by weight are completely amorphous. In the present invention, a polymer having a high vinyl acetate content, specifically, an amorphous ethylene-vinyl acetate copolymer having 40 to 90% by weight of vinyl acetate groups is used. Particularly preferred are 55-70% by weight of polymer. The reason is that when using such polymers,
This is because a foam having a particularly high expansion ratio can be obtained. In the present invention, not only the above-mentioned ethylene-vinyl acetate copolymer is used as the resin component, but also other blendable thermoplastic resins may be blended. In particular, when the ethylene-vinyl acetate copolymer is an amorphous polymer, it is preferable to blend it with a crystalline polymer. There is no particular limit to the blending ratio, but it is usually 20 to 80%. As the thermoplastic resin used at this time, all kinds of commercially available polymers can be used, but olefin-based polymers, especially ethylene-based polymers, are the most preferred in terms of compatibility and processability. polyethylene, ethylene-α-olefin copolymer,
These include ethylene-propylene copolymers, ethylene-vinyl acetate copolymers with a vinyl acetate content of 5 to 30%, ethylene-ethyleacrylate copolymers, ethylene-vinyl acetate-vinyl chloride copolymers, and the like. In the present invention, the best foam can be obtained by blending a crystalline ethylene-vinyl acetate copolymer or polyethylene with a non-crystalline ethylene-vinyl acetate copolymer having a vinyl acetate content of 5 to 30%. In the present invention, the inorganic powder is not particularly limited, but includes, for example, hydrated metal oxides such as aluminum hydroxide, magnesium hydroxide, and basic magnesium carbonate, metal oxides such as alumina and titania, calcium carbonate, and carbonate. Carbonates and bicarbonates such as magnesium, sodium bicarbonate,
Borate such as zinc borate, borax, barium borate,
These include phosphates such as calcium phosphate and potassium metaphosphate, silicates and silicic acids such as talc and clay, sulfates and sulfites such as gypsum, and residues such as blast furnace slag and red mud. Further, when it is desired to obtain a flame-retardant foam, a hydrated metal oxide is used, and the above-mentioned aluminum hydroxide, magnesium hydroxide, and basic magnesium carbonate are preferably used. In particular, aluminum hydroxide is preferred because it exhibits a high degree of flame retardancy in a mixture with an ethylene-vinyl acetate copolymer. The particle size of inorganic powder is usually 0.01μ to 30μ, preferably
A range of 0.05 to 10μ, particularly 0.1 to 2μ, is desirable. If the particle size exceeds this upper limit, the extrusion-molded sheet will have a rough surface and the expansion ratio will decrease. Moreover, if it is smaller than this lower limit, it will be difficult to reproduce a uniform dispersion state, and the expansion ratio will decrease. The amount of this inorganic powder added is 50 to 500 parts by weight, preferably 80 to 250 parts by weight, particularly preferably 100 to 200 parts by weight.
Parts by weight. The reason is that if the amount is less than the lower limit, the effect of adding the inorganic substance cannot be exhibited, and if it is more than the upper limit, it becomes difficult to achieve high foaming. In addition, the blowing agents to be blended in the method of the present invention include various organic and inorganic decomposition type blowing agents, and examples of the organic blowing agents include azodicarbonamide,
N,N'-dinitrosopentamethylenetetramine,
P,P'-oxybisbenzenesulfonyl hydrazide and the like. Examples of inorganic blowing agents include sodium bicarbonate, ammonium carbonate, ammonium bicarbonate, and calcium azide. The reason for limiting the amount added to 5 to 50 parts by weight is 5.
If the amount is less than 50 parts by weight, it will not be possible to obtain a highly foamed product, and if it exceeds 50 parts by weight, it will not contribute to improving the expansion ratio and the efficiency will deteriorate significantly. Note that a so-called foaming aid may be added in order to adjust the decomposition temperature of the foaming agent. Furthermore, in the present invention, a crosslinking accelerator can be added if necessary. The amount added is usually 0.05
~10 phr, preferably 0.1-2.0 phr. As the crosslinking accelerator, polyfunctional compounds such as cyanurate compounds such as triaryl isocyanurate and triaryl cyanurate, monoacrylate and monomethacrylate compounds such as methoxydiethyl glycol methacrylate, diethylene glycol dimethacrylate, polyethylene glycol dimethacrylate, 1.6- Diacrylates and dimethacrylate compounds such as hexane glycol diacrylate, 2.2-bis(4-acryloxydiethoxyphenyl)propane, triacrylates such as trimethylolpropane trimethacrylate, trimethylolpropane triacrylate, and tetramethylolmethane triacrylate and aromatic compounds having unsaturated bonds such as trimethacrylate compounds, tetraacrylate compounds such as tetramethylolmethanetetraacrylate, polybutadiene compounds such as 1,2-polybutadiene, maleic acid esters such as divinyl maleate and dipropargyl maleate, and divinylbenzene. Compounds, etc. Among these, trifunctional or tetrafunctional acrylates or methacrylates are preferred. Furthermore, since the present invention contains a large amount of inorganic substance, a surface treatment agent such as a silane surface treatment agent or a titanate type surface treatment agent may be used to improve the compatibility between the inorganic substance and the resin, and these are particularly preferred. is isopropyl triisostearoyl titanate, isopropyl trioctanoyl titanate,
These are monoalkoxy titanate compounds such as isopropyl distearoyl methacrylic titanate and isopropyl diisostearoyl acrylic titanate. Use of these surface treatment agents facilitates the kneading and molding work of the mixture and improves the foaming rate. In addition, the method of the present invention may optionally include halogen flame retardants such as decabromodiphenyl oxide (the amount added is usually 5 to 30 phr) and flame retardant aids such as antimony trioxide (the amount added is usually 2 to 20 phr). ), antioxidants, copper inhibitors, antistatic agents, colorants, pigments, lubricants, and other processing aids may be added. In the present invention, when it is desired to obtain a foam with particularly excellent flame retardancy, aluminum hydroxide,
In addition to using hydrated metal oxides such as magnesium hydroxide and basic calcium carbonate, so-called halogen flame retardants are also used. In this case, hydrates such as aluminum hydroxide not only improve flame retardancy, but also play a major role in reducing smoke generation, which has significantly increased due to the addition of halogen flame retardants. A flammable foam will be obtained. Foams that have contradictory properties, such as high flame retardancy and low smoke generation, are desired as thermal insulation materials for buildings and the like. JIS A1321- mentioned above
1975 “Flame retardant test method for building interior materials and construction methods”
Tests based on this measure evaluate exactly this kind of performance. In this case, it is particularly preferable to use the following halogen flame retardants. That is, it has a prom content of 40 to 80% by weight and has two or more repeating units in its chemical structural formula. For example, bisphenol A tetrabromobisphenol A epichlorohydrin glycidyl etherified condensate, tetrabromobisphenol A diglycidyl ether and brominated bisphenol adduct, poly-4,4-isopropylidene bis(2,6-dibromophenyl) carbonate It is. Specific products of these flame retardants include, for example, Matsunaga Chemical Co., Ltd.'s EBR-700 (bromine content: approximately 52% by weight), Teijin Kasei Co., Ltd.'s product,
FIREGUARD7000 series (brome content approx. 50
(wt%), Hitachi Chemical Co., Ltd. product HR-128F (brome content approximately 50 wt%), etc. Next, particular points to be noted regarding the method of crosslinking using ionizing radiation of the present invention will be explained. In the case of the present invention, it is essential that the resin component has as a main component a non-crystalline ethylene-vinyl acetate copolymer having a vinyl acetate content of 40 to 90% by weight. When blending thermoplastic resins, polyethylene, crystalline ethylene-vinyl acetate copolymer with a vinyl acetate content of 5 to 30% by weight, ethylene-vinyl acetate-vinyl chloride copolymer, ethylene-ethyl acrylate It is preferable to blend 50% by weight or less of an ethylene polymer such as a copolymer. Furthermore, in the case of this method, 1 to 5 parts by weight of carboxylic acid metal salts (salts of carboxylic acids such as stearic acid, capric acid, caproic acid, lauric acid, and acetic acid with zinc, lead, and aluminum) are added. Usually, these are added as lubricants of about 1 phr, but in the case of the present invention, they are not only used as lubricants, but also as necessary to improve the foaming ratio and to obtain highly foamed products, as shown in the examples. This shows the effect of reducing the optimal irradiation dose. For this purpose, it is preferable to add about 2 to 4 phr, and zinc stearate and lead stearate are particularly suitable. Next, a specific example of the manufacturing process of the foam of the present invention will be explained. The polymer, inorganic powder, blowing agent, flame retardant and flame retardant aid if necessary, and other necessary additives are measured and kneaded. Banbury mixer, kneader mixer or two roll mill,
In some cases, a twin screw extruder is used. Normally, after kneading, the pellets are formed into a sheet using an extruder, but in some cases, the pellets are directly extruded into a sheet from a twin-screw extruder or the like to form a molded product. Crosslinking can be carried out simply by irradiating the obtained extruded sheet with an electron beam of 1 to 5 Mard. Next, it is introduced into a heating device for foaming, such as a hot air oven, an infrared heating furnace, or a molten salt bath, to obtain a continuous foam sheet. Although it varies depending on the size of the device, it is usually a sheet-like foam with a thickness of 2 to 20 mm and a width of 1000 to 1500 mm. The foam obtained by the method of the present invention can be used for various purposes by taking advantage of its characteristics. Formed into a pipe shape and used as a pipe cover for insulation, sheet shaped as a packaging material,
Not only can it be used as packing material, cushioning material, costume material, flotation material, etc., but also for construction, where there are strict legal regulations regarding the flame retardance and smoke emitting properties of materials due to their low smoke and flame retardant characteristics. It is used for materials, automobile materials, railway vehicle materials, ships and aircraft materials, etc. It is also used in a composite state with a metal plate such as an iron plate, a metal foil, or an inorganic material in the form of a fiber, plate, or film. Next, examples of the present invention and comparative examples will be shown. (All parts and % below are parts by weight and % by weight.) Examples 1 to 3, Comparative Examples 1 to 3 Ethylene-vinyl acetate copolymer with a vinyl acetate content of 61% (Dainippon Ink Chemical Kogyo Co., Ltd. products:
Everthrene 450-P) and crystalline ethylene-vinyl acetate copolymer with a vinyl acetate content of 25% (Mitsui Polychemical Co., Ltd. product: Evaflex 360)
Blend ratio of 100/0, 80/20 and 60/40
Aluminum hydroxide powder (Showa Denko Co., Ltd. product: Hygilite H-
42M) 100 parts, blowing agent azodicarbonamide (Eiwa Kasei Co., Ltd. product: Vinihole AC) 23 parts,
Flame retardant decabromodiphenyl ether (Toyo Soda Co., Ltd. product: EB-10FP) 20 parts antimony trioxide (Nippon Seiko Co., Ltd. product) 8 parts and titanate coupling agent (Kenrich
Petrochemical product: KEN-REACT TTS)
3 parts were added, uniformly kneaded using a Brabender Plastograph, and formed into a sheet with a thickness of 1 mm using a hot press. Next, in an electron beam irradiation device, 1
After being subjected to electron beam irradiation treatment at ~4 Mrad, the foam was heated at 200°C for 15 minutes in a hot air constant temperature bath to obtain a foam.
The results are shown in Table 1. Examples 1 to 3 have the above compositions in which 1 part of zinc stearate (reagent) was added, and Comparative Examples 1 to 3 have compositions that do not contain zinc stearate. From the comparison of Comparative Examples 1 to 3, it can be seen that as the blend ratio of crystalline EVA increases, the expansion ratio decreases. And, as in Examples 1 to 3, it can be seen that when zinc stearate is added, the expansion ratio is significantly improved in all compositions, and the effect is particularly shown when the blend ratio of crystalline EVA is large.
Furthermore, it can be seen that the addition of zinc stearate shifts the irradiation dose that gives the highest expansion ratio to a lower dose.

【table】

[Table] Examples 4 to 7, Comparative Example 4 The resin components were 70 parts of ethylene-vinyl acetate copolymer (same as Example 1) and ethylene-vinyl acetate-vinyl chloride terpolymer (product of Nippon Zeon Co., Ltd.) The same composition as in Examples 1 to 3 except that it consisted of 30 parts of graftomer GR-5) and a predetermined amount of various stearates was irradiated and foamed in the same manner. The results are listed in Table 2 together with the main components of the composition. Example 4 in which 1 to 3 parts of stearate was added compared to Comparative Example 4 which did not contain stearate metal salt.
-7, the foaming ratio was significantly improved, and the optimum irradiation dose was reduced to around 2 Mrad, making it extremely efficient. The effects of zinc stearate and lead stearate are particularly pronounced.

【table】

【table】

Claims (1)

[Claims] 1. Ethylene containing 40 to 90% by weight of vinyl acetate
100 parts by weight of a resin consisting of a vinyl acetate copolymer alone or a blend of the copolymer and a thermoplastic resin;
After molding a composition containing 50 to 500 parts by weight of an inorganic powder, 5 to 50 parts by weight of a blowing agent, and 1 to 5 parts by weight of a carboxylic acid metal salt, the composition is crosslinked by irradiation with ionizing radiation, and then the decomposition temperature of the blowing agent is determined. 1. A method for producing an inorganic-containing ethylene-vinyl acetate copolymer foam, which comprises foaming by heating to the above temperature. 2 The thermoplastic resin is polyethylene, ethylene-
α-olefin copolymer, vinyl acetate content 5~
30% by weight of one or more of the group consisting of crystalline ethylene-vinyl acetate copolymer, ethylene-vinyl acetate-vinyl chloride copolymer, ethylene-ethyl acrylate copolymer, and ethylene-propylene copolymer 2. The method for producing a foam according to claim 1, wherein the foam is an ethylene polymer. 3. The method for producing a foam according to claim 1, wherein the composition further contains 5 to 30 phr of a flame retardant and 2 to 20 phr of a flame retardant aid. 4. The method for producing a foam according to claim 3, wherein the flame retardant has a bromine content of 40 to 80% by weight and has two or more repeating units in its chemical structural formula.